Heretofore, a flexible polyurethane foam has been used for various applications. For example, it is possible to use it widely for from various industrial products to daily use products, such as beddings such as mattresses or cushions, furniture, seat cushions or seat back materials for cars or parts for headrests or armrests. Further, by glueing it to other materials such as cloths or leathers, it is widely used as epidermis materials of cushioning car seats, ceiling materials, top layer materials of sofas as furniture or top layer materials of beds.
However, a flexible polyurethane foam is flammable, and it has been desired to make it flame-retardant. The degree of flame retardancy varies depending on the particular application of the flexible polyurethane foam, and it is required to pass a relatively difficult flammability test, such as Flammability Test of Interior Decorating Materials for Cars (FMVSS-302), Flammability Test of Materials for Electricity, U.S.A. (UL94), Flammability Test of Materials for Railroad Axles (Standards of Department of Transportation, Standard A-A) or Flammability Test for Space Fillers for Seat Cushions of Air Planes (FAR25853(c)). In recent years, a flexible polyurethane foam has been used as a component of an office automation equipment or a component for an electrical apparatus, and a low flammability is required depending on such an application. For example, the Flammability Test of Materials for Electricity, U.S.A. (UL94) has commonly been used as an index for flammability in order to use the foam as a component for an electrical apparatus. According to the specification, it is required to reduce dripping of the flexible polyurethane foam during combustion, as far as possible, and in order to pass the specification, it is necessary to overcome the problem of easiness of carbonization of the flexible polyurethane foam.
Heretofore, the method for making a flexible polyurethane foam flame-retardant may, for example, be a method to foam raw material for the flexible polyurethane foam, which contains a flame retardant. The flame retardant may, for example, be an organic flame retardant such as a halogen-containing compound, a phosphate ester compound or a halogen-containing phosphate ester compound. For example, as an organic flame retardant, such as a phosphate ester compound or a halogen-containing phosphate ester compound, TCEP (tris(chloroethyl) phosphate), TCPP (tris(chloropropyl) phosphate) or TCP (tricresyl phosphate) is an adding-type flame retardant having no active hydrogen which reacts with an isocyanate group. Accordingly, it does not affect the foaming reaction, and it is easy to be used, since it is liquid. It also has a high flame-retardant effect, and by increasing its amount to be used, it is possible to expect improvement in flame retardancy. However, if the amount of the flame retardant is increased, there is an adverse affect on moldability of a flexible polyurethane foam (Patent Documents 1 and 2).
Further, it is also possible to consider using an inorganic type flame retardant such as aluminum hydroxide, antimony trioxide, zinc oxide or expandable graphite, as a flame retardant. However, if the inorganic type flame retardant is used, usually, there are many cases wherein the sufficient amount may not be added because of remarkable viscosity increase of the raw material system. Further, expandable graphite has a characteristic such that it rapidly expands when heated, and by using such a characteristic, it is possible to suppress combustion and to prevent further combustion. However, it is an acidic substance, whereby if it is contained in a raw material for a flexible polyurethane foam in a large amount, a basic urethane-forming catalyst is deactivated, thereby leading to deterioration of a reactivity for a urethane-formation, and as a result, there is an adverse affect on foaming property (Patent Document 3).
In order to solve the above problem, the following techniques have been proposed. Namely, a method to obtain a low-flammable flexible polyurethane foam by selecting diphenylmethane diisocyanate (MDI) having an isocyanate index in a specific range, a melamine resin and liquid form phosphorus type compound as flame retardants and a dimethyl polysiloxane/polyoxyalkylene copolymer having a hydroxyl group at a polyether terminal, as a foam stabilizer (Patent Document 4), a method to impart flame retardancy by immersing a plate-form body cut out from a flexible polyurethane slab foam in an emulsion containing an acryl type resin, a polyvinyl chloride and carbon black, as dispersed (Patent Document 5) and a method to obtain a fine cell structure polyurethane elastomer by adding a flame retardant, a crosslinking agent, a foam stabilizer and a foaming component to an isocyanate-terminal prepolymer, followed by mixing, foaming and curing (Patent Document 6).
However, each one of them is a method of improving flame retardancy by using a conventional flame retardant or further modifying the isocyanate, and such a method does not have sufficient productivity because the production cost is thereby high and it has many production steps. Further, it does not satisfy the demands for both flame retardancy and moldability at the same time.
Further, in the application as e.g. a component of an office automation equipment or a component for an electrical apparatus, a foam less susceptible to deterioration by ultraviolet rays and having good weather resistance in addition to the above mentioned flame retardancy, is needed. As the method to improve weather resistance of a flexible polyurethane foam, a method of adding a polyester polyol, is known (Patent Document 7). However, the flame retardancy is not mentioned, or the weather resistance of a foam using a conventional flame retardant, is not mentioned. Further, the demands for both weather resistance and flame retardancy have not been satisfied at the same time.
On the other hand, a method for producing a flexible polyurethane foam using a polyol which is produced by using a double metal cyanide complex catalyst, is known (Patent Documents 8, 9 and 10). However, the influence of the double metal cyanide complex catalyst contained in the polyol used, is not mentioned. Further, the flame retardancy of the obtained flexible polyurethane foam is not mentioned either.    Patent Document 1: JP-A-2005-301000    Patent Document 2: JP-A-2005-15521    Patent Document 3: JP-A-2002-3713    Patent Document 4: JP-A-2001-200028    Patent Document 5: JP-A-9-262912    Patent Document 6: JP-A-2005-29617    Patent Document 7: JP-A-10-25327    Patent Document 8: JP-A-2004-269850    Patent Document 9: JP-A-2003-522235    Patent Document 10: JP-A-2004-530767